Recently, many communication applications use, as a de facto standard, a TCP (Transmission Control Protocol) protocol corresponding to a protocol of a transport layer in an OSI reference model, and there are various variations of the TCP protocol having different characteristics.
The Internet in recent years has continued to progress, for example, the speed the network and the distances covered by the network are increasing, and an LFN (Long Fat Network) and a wireless access network are becoming popular. An LFN has a problem in that in spite of having a wide bandwidth, sufficient performance is not exhibited because the TCP is applied between the communication devices, and a TCP that has been improved for LFNs has appeared. Furthermore, in the case of going through a wireless network, there is a problem in that throughput does not increase as a result of a packet error having occurred in the wireless network being recognized as congestion from the viewpoint of the TCP, and an improvement has been added to a TCP that deals with such a problem. As described above, the TCP protocol has repeatedly improved communication performance in response to the progress of network environments. As a result, various improved versions or variants, which have been specialized for a usage environment, exist.